The invention relates generally to the arrangement of telecommunication on the channels between base stations and terminals of a cellular system. Particularly the invention relates to an efficient utilisation of the communication capacity contained in the channels.
According to the official definition by CCITT (Comitxc3xa9 Consultatif International Txc3xa9lxc3xa9phonique et Txc3xa9lxc3xa9graphique) a xe2x80x9cchannelxe2x80x9d is an identified portion of an interface. In cellular systems the radio interface between a base station and the terminals contains several channels. Of these channels the downlink paging channel, the broadcast control channel, and the cell broadcast channel are the essential channels regarding this invention. A known embodiment of these channels in the GSM system (Global System for Mobile telecommunications) is described below in order to clarify the background of the invention.
In the GSM system the radio interface is divided into frequency bands with a width of 200 kHz, which in the time direction is divided into time slots with a length of 0.577 ms, and the information is transmitted as bursts in these time slots. The definition of a certain channel represents the indication of those time slots which can transmit information belonging to said channel. The Paging CHannel (PCH) and the Access Grant CHannel (AGCH) create a PAGCH entity, where the proportions of the PCH and the AGCH will vary with time. The Broadcast Control CHannel (BCCH) is a channel of its own. The time slots used by the BCCH and the PAGCH are defined as follows: at the so called Common Control CHannel (CCCH) frequency of the cell there are taken 51 successive frames each formed by eight successive time slots, and from each frame the first time slot is taken. The time slots obtained in this way are numbered from 0 to 51. Then the time slots 2 to 5 belong to the BCCH and the time slots 6 to 9, 12 to 15, 16 to 19, 22 to 25, 26 to 29, 32 to 35, 36 to 39, 42 to 45 and 46 to 49 belong the PAGCH, if the so called full rate PAGCH is used. A PAGCH of the one third rate comprises only the time slots 6 to 9, 12 to 15 and 16 to 19.
The Cell Broadcast CHannel (CBCH) can be located on the same frequency together with the BCCH and the PAGCH, or on another frequency, or it can even use frequency hopping. It is defined so that when one examines eight successive periods of 51 frames, having a total length of about 2 seconds, then the CBCH during this period comprises four groups formed by four time slots. Regarding the time slots used by the PAGCH the time slots used by the CBCH are located so that there is always a time difference of at least a certain minimum length between a burst transmitted in a time slot belonging to the CBCH and the burst which belongs to a paging message and which is transmitted in a time slot belonging to the PAGCH, so that a terminal can receive both the bursts transmitted through the CBCH and the paging messages. The arrangement of the time slots used by BCCH, PAGCH and CBCH is described in more detail for instance in the book Michel Mouly, Marie-Bernadette Pautet: xe2x80x9cThe GSM System for Mobile Communicationsxe2x80x9d, published by the authors, ISBN 2-9507190-0-7, Palaiseau 1992.
All terminals in a certain cell do not receive all paging messages transmitted on the PAGCH, but the terminals have been divided into so called paging groups, and the paging messages transmitted to these groups have a certain schedule within the PAGCH. When a terminal is in the idle mode its receiver is always active and tuned to the CCCH frequency when its paging group has a scheduled paging message transmission time. Further the receiver of a terminal is always active and tuned to the CCCH frequency during the BCCH and the CBCH.
When the receiver of a terminal is on it consumes energy. The receiver should be on as little of the time as possible, so that the charge of the terminal""s battery could last longer.
The object of the invention is to present a method with which the electric power consumption of a terminal""s receiver can be reduced in the idle mode, compared to prior art. An object of the invention is also to present devices for using the method according to the invention.
The object of the invention is achieved so that information, which usually is transmitted on the broadcast control channel and on the cell broadcast channel, is placed in unoccupied parts of the paging channel.
The method according to the invention is applicable in a cellular system, where between a base station and a terminal there is defined a paging channel for transmitting the requests for establishing downlink connections, and a broadcast control channel for transmitting general information concerning the cell of the base station. The method according to the invention is characterised in that general information concerning the base station""s cell are transmitted on the paging channel when the paging channel""s data transmission capacity is higher than the total amount of data which has to be transmitted concerning the requests to establish downlink connections.
The invention relates also to a cellular system base station which is characterised in that it comprises means for transmitting general information on the paging channel concerning the base station""s cell.
Further the invention relates to a cellular system terminal which is characterised in that it comprises means for receiving general information on the paging channel concerning the base station""s cell.
The paging channel comprises certain time slots (more generally: certain time periods on a certain frequency), during which the terminals must be in the receiving mode, regardless of whether or not the base station in fact has paging messages to be transmitted. According to the invention the base station can transmit other information in those parts of the paging channel, which otherwise would be unoccupied due to the low number of paging messages to be transmitted. The other information is preferably that information, which normally is transmitted on the broadcast control channel and/or on the cell broadcast channel. When the terminal receives on the paging channel information, which belongs to the broadcast control channel and/or to the cell broadcast channel, then it is not necessary for it to receive the same information again on the proper broadcast control channel and/or on the cell broadcast channel, but it can switch its receiver off for the time of the transmission of other channels, and thus it can save power.
Power saving in a base station is not as essential as in the terminals, so a base station can quite well transmit the same information both in the unoccupied parts of the paging channel and on the broadcast control channel and/or on the cell broadcast channel.